U.S. patent number 6,364,616 [Application Number 09/567,553] was granted by the patent office on 2002-04-02 for submerged rib hybrid blade.
This patent grant is currently assigned to General Electric Company. Invention is credited to Wendy Wen-Ling Lin, Joseph Timothy Stevenson.
United States Patent |
6,364,616 |
Stevenson , et al. |
April 2, 2002 |
Submerged rib hybrid blade
Abstract
A fan blade includes a metal airfoil having a pocket disposed in
a first side thereof, with the pocket including a filler bonded
thereto. The pocket includes a plurality of cells separated by
corresponding ribs which are submerged in the filler.
Inventors: |
Stevenson; Joseph Timothy
(Amelia, OH), Lin; Wendy Wen-Ling (Niskayuna, NY) |
Assignee: |
General Electric Company
(Cincinnati, OH)
|
Family
ID: |
24267629 |
Appl.
No.: |
09/567,553 |
Filed: |
May 5, 2000 |
Current U.S.
Class: |
416/233; 416/224;
416/229A; 416/241A; 416/229R |
Current CPC
Class: |
B64C
11/00 (20130101); F01D 5/147 (20130101); F01D
5/16 (20130101); F05D 2250/711 (20130101); Y02T
50/60 (20130101); F05D 2250/292 (20130101); Y02T
50/672 (20130101); Y02T 50/673 (20130101) |
Current International
Class: |
B64C
11/00 (20060101); F01D 5/16 (20060101); F01D
5/14 (20060101); B64C 011/16 () |
Field of
Search: |
;416/224,241A,235,233,229R,232,500,230,229A,144,145 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Look; Edward K.
Assistant Examiner: Woo; Richard
Attorney, Agent or Firm: Hess; Andrew C. Herkamp; Nathan
D.
Claims
Accordingly, what is desired to be secured Letters Patent of the
United States is the invention as defined and differentiated in the
following claims in which we claim:
1. A gas turbine engine fan blade comprising:
a metal airfoil having first and second opposite sides extending
radially between a root and a tip, and axially between a leading
edge and a trailing edge for pressurizing air channeled
thereover;
said airfoil further including a pocket disposed in said first
side, and having a perimeter extending along a border of said first
side around said leading and trailing edges, root, and tip;
said pocket including a plurality of cells separated by
corresponding ribs; and
a filler bonded in said pocket, with said ribs being submerged
therein, to define an exposed outer surface of said filler over
said ribs.
2. A blade according to claim 1 wherein said ribs are convex in
section.
3. A blade according to claim 2 wherein said ribs have tapered
sides blending with said cells.
4. A blade according to claim 3 wherein said ribs are submerged in
said filler within the range of about 0.5-2.5 mm, and said filler
defines an exposed portion of said airfoil first side coextensive
with said border.
5. A blade according to claim 1 wherein said pocket includes a
shelf around said perimeter blending with said border.
6. A blade according to claim 5 wherein said shelf is tapered from
said border inwardly into said pocket.
7. A blade according to claim 6 wherein said shelf is tapered to
said submerged ribs and along adjoining cells thereat.
8. A blade according to claim 7 wherein said shelf is continuous
around said pocket perimeter and border.
9. A blade according to claim 7 wherein said shelf has a different
taper than said cells thereat.
10. A blade according to claim 1 wherein:
said ribs are convex in section; and
said pocket includes a shelf around said perimeter blending with
said border.
11. A blade according to claim 10 wherein:
said ribs have tapered sides blending with said cells; and
said shelf is tapered from said border inwardly into said
pocket.
12. A blade according to claim 11 wherein said rib taper is
different than said shelf taper.
13. A blade according to claim 12 wherein said rib taper is greater
than said shelf taper.
14. A blade according to claim 13 wherein said shelf taper is less
than a taper of said cells thereat.
15. A blade according to claim 11 wherein:
said rib taper is less than or equal to about 60 degrees;
said shelf taper is shallow, and less than or equal to about 20
degrees; and
wherein said ribs are submerged in said filler within the range of
about 0.5-2.5 mm, and said filler defines an exposed portion of
said airfoil first side coextensive with said border.
16. A gas turbine engine fan blade comprising: a metal airfoil
having first and second opposite sides extending radially between a
root and a tip, and axially between a leading edge and a trailing
edge for pressurizing air channeled thereover;
said airfoil further including a pocket disposed in said first
side, and having a perimeter extending along a border of said first
side around said leading and trailing edges, root, and tip;
said pocket including a plurality of cells separated by
corresponding ribs being convex in section, and said pocket
includes a shelf around said perimeter blending with said border,
and said shelf is tapered from said border inwardly into said
pocket; and
a filler bonded in said pocket, with said ribs being submerged
therein.
17. A blade according to claim 16 wherein said ribs are
substantially equally submerged in said filler.
18. A blade according to claim 17 wherein said filler is flush with
said border, and defines therewith a continuous surface exposed to
said air channeled thereover.
19. A blade according to claim 18 wherein said filler is
elastomeric bonded to a primer covering said cells, ribs, and
shelf.
20. A blade according to claim 19 further comprising:
a shank joined integrally with said airfoil root; and
a dovetail joined integrally with said shank for mounting said
blade to a rotor disk.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to gas turbine engines,
and, more specifically, to wide chord fan blades therein.
A turbofan gas turbine engine includes a row of fan blades powered
by a low pressure turbine (LPT). Air initially enters the engine
through the fan, and an inner portion thereof enters a compressor
which pressurizes the air for mixing with fuel in a combustor, with
the mixture being ignited for generating hot combustion gases that
flow downstream through a high pressure turbine (HPT) that extracts
energy for powering the compressor. The combustion gases then flow
through the LPT which extracts additional energy therefrom for
powering the fan. The remaining outer portion of the air flowing
through the fan is discharged from the engine for producing thrust
to power an aircraft in flight.
A fan blade includes a dovetail at its radially inner end which is
trapped in a complementary dovetail slot in the perimeter of a
rotor disk. An airfoil is attached to the dovetail by a structural
shank. Platforms may be joined integrally with the blade or
separately attached between adjacent blades for providing a
radially inner flowpath boundary for the fan air, with the platform
being radially located atop the shank at a radially inner root of
the airfoil.
The airfoil extends radially outwardly to an opposite tip, and has
a forward or leading edge and an axially opposite aft or trailing
edge collectively defining the perimeter of the airfoil. The
airfoil has a generally concave, pressure first side and a
circumferentially opposite, generally convex, suction second side.
The airfoil has a span or longitudinal axis extending in the radial
direction from the centerline of the rotor disk to which it is
attached, and various chords extending generally axially between
the leading and trailing edges. The airfoil typically twists from
its root to its tip for maximizing aerodynamic performance.
A wide chord fan blade has a relatively low aspect ratio which is
its span to chord ratio, and is relatively heavy when formed as a
solid metal part. Weight reduction is typically obtained by using
high strength superalloy materials such as those including
titanium. However, as engines grow larger in size, the
corresponding fan blades increase in size and weight, and increase
the difficulty in achieving a suitable life therefor under the high
centrifugal loads generated during operation.
In separate developments, all-composite fan blades have been
designed for reducing weight while providing acceptable performance
in the gas turbine engine environment. A typical composite blade
includes several layers of structural fibers, such as graphite,
embedded in a suitable matrix, such as epoxy, for tailoring blade
strength in a lightweight structure. Composite blades require a
complex manufacturing process and are expensive to produce.
Hybrid blades are also being developed which are primarily metal,
such as titanium, having suitable pockets therein for reducing
weight, with the pockets being filled with a suitable elastomeric
filler material for completing the required aerodynamic profile of
the airfoil. The pockets are defined by corresponding integral
metal ribs which provide metal across the full thickness of the
airfoil for maximizing the remaining stiffness and bending moment
of inertia of the airfoil.
However, the weight-reducing pockets necessarily interrupt the
structural continuity of the airfoil, with the exposed edges of the
pockets creating structural discontinuities in the airfoil surface
adjoining the filler material. The ribs are therefore subject to
local stress concentration during operation.
During operation, the fan blades rotate and are subject to
centrifugal loads which are carried by the metal portion of the
airfoils including the ribs, with the filler merely providing dead
weight which in turn is carried by the metal portion of the
airfoil. The airfoil is subject to vibratory bending and torsion
which in turn increases the loads and resulting stress carried by
the metal airfoil including the ribs thereof. And, the fan blade is
subject to foreign object damage (FOD) due to impact from a bird
strike for example. A bird strike subjects the blade to additional
shock loading which further increases the stress of the metal
airfoil including the ribs.
In order to ensure a strong bond between the filler and the
underlying metal of the airfoil, a primer coat may be applied in
the pockets prior to filling with the filler material. When the
filler is cured and bonded to the metal airfoil, its outer surface
is directly exposed to the ambient air and is coextensive or flush
with the remaining metal border of the airfoil for defining the
corresponding aerodynamically configured side of the airfoil.
However, the underlying primer is exposed along the edge interface
between the filler and the metal border and is therefore subject to
degradation due to humidity, chemical solvents, and handling
damage. Degradation of the primer can then lead to delamination of
the filler from the metal airfoil, and a corresponding reduction in
useful life of the fan blade.
Accordingly, it is desired to provide an improved hybrid fan blade
having reduced stress concentrations and reduced exposure of the
filler-metal interface.
BRIEF SUMMARY OF THE INVENTION
A fan blade includes a metal airfoil having a pocket disposed in a
first side thereof, with the pocket including a filler bonded
thereto. The pocket includes a plurality of cells separated by
corresponding ribs which are submerged in the filler.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, in accordance with preferred and exemplary
embodiments, together with further objects and advantages thereof,
is more particularly described in the following detailed
description taken in conjunction with the accompanying drawings in
which:
FIG. 1 is an elevational view of an exemplary gas turbine engine
hybrid fan blade including a multi-cell pocket including a filler
therein in accordance with an exemplary embodiment of the present
invention.
FIG. 2 is a radial sectional view through a mid-span portion of the
airfoil illustrated in FIG. 1 and taken generally along line
2--2.
FIG. 3 is an enlarged radial sectional view of an exemplary
submerged rib of the airfoil illustrated in FIG. 2 within the
dashed circle labeled 3.
FIG. 4 is an enlarged radial sectional view of the pocket adjoining
the metal border near the leading edge as shown within the dashed
circle labeled 4 of FIG. 2 in accordance with an exemplary
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Illustrated in FIG. 1 is one of several exemplary turbofan gas
turbine engine fan rotor blades 10 mounted to the perimeter of a
rotor disk 12 shown in part. In accordance with the present
invention, the blade is configured as a hybrid blade including a
metal airfoil 14 having a first or pressure side 16 which is
generally concave, and a circumferentially opposite second or
suction side 18 which is generally convex. The first and second
sides or surfaces 16, 18 extend radially along the span of the
airfoil between a radially inner root 20 and an opposite radially
outer tip 22.
The first and second sides also extend axially along the chords of
the airfoil between a forward or leading edge 24, and an axially
opposite aft or trailing edge 26. Ambient air 28 flows over the two
airfoil sides from the leading edge to the trailing edge during
operation and is pressurized by the airfoil in a conventional
manner for producing propulsion thrust for powering an aircraft in
flight.
Although the airfoil 14 may be integrally or directly mounted to
the rotor disk 12 in a one-piece assembly known as a blisk, in the
exemplary embodiment illustrated in FIG. 1 each of the airfoils is
removably attached to the disk in a conventional manner. For
example, the blade further includes a metal shank 30 joined
integrally with the airfoil root 20 for mounting the blade to the
rotor disk 12. This is effected using a conventional metal dovetail
32 joined integrally with the shank for mounting the blade in a
complementary dovetail slot 12a in the rotor disk. The airfoil 14,
shank 30, and dovetail 32 may be initially formed as a one-piece or
unitary metal structure such as by forging. A suitable metal for
the fan blade is titanium, for example.
The dovetail 32 is typically an axial-entry dovetail which is
captured in a complementary axial dovetail slot 12a in the
perimeter of the rotor disk. The shank 30 provides a structural
transition from the dovetail to the aerodynamic airfoil, and is
typically not an aerodynamic member itself. The shank is typically
hidden from the airflow by a suitable flow bounding platform (not
shown) disposed at the airfoil root 20 either integrally therewith
or as separately mounted platforms between adjacent ones of the
blades in a conventional manner.
In accordance with the present invention, the airfoil 14 includes a
recess or pocket 34 preferably disposed solely in the airfoil first
or pressure side 16, with the pocket having a full four-sided
perimeter 34a extending along a border 16a of the airfoil first
side around the leading and trailing edges 24, 26, root 20, and tip
22.
The pocket 34 includes a plurality of compartments or cells 34b
separated from each other by corresponding metal ribs 36. In the
exemplary embodiment illustrated in FIG. 1, multiple chordal and
radial ribs 36 intersect each other for defining five exemplary
pocket cells 34b.
The entire pocket including its cells includes an elastomeric
filler 38 suitably bonded therein, with the ribs 36 being recessed
or submerged in the filler below the exposed surface thereof.
The basic airfoil 14 illustrated in FIG. 1 is metal for providing
structural integrity for withstanding aerodynamic, centrifugal, and
vibratory loads during operation as the fan blade rotates for
producing propulsion thrust by pressurizing the air 28. The pocket
including its cells is provided in the airfoil for substantially
reducing the overall weight thereof, and reducing the centrifugally
generated loads during operation. The filler 38 is relatively
lightweight and may take any suitable form such as elastomeric
rubber or polyurethane for filling the pocket to provide a
continuous surface over the airfoil first side which is exposed to
the airflow 28 for pressurization thereof.
FIG. 2 illustrates an exemplary radial sectional view through a
portion of the airfoil illustrated in FIG. 1, with the metal
airfoil and blade being continuous from the leading edge 24 to the
trailing edge 26, as well as being continuous from the dovetail 32
to the airfoil tip 22 as illustrated in FIG. 1. As shown in FIG. 2,
the leading and trailing edges 24, 26 are relatively thin and sharp
for maximizing aerodynamic efficiency and are completely metal
between the suction side 18 and the border portion 16a of the
pressure side 16 for maintaining strength and structural integrity
of the airfoil, notwithstanding the introduction of the pocket 34
including its several cells.
The cells 34b are defined around their perimeters by respective
ones of the ribs 36 and the corresponding portions of the first
side border 16a. The collective profile of the airfoil 14
illustrated in FIG. 2 defines between its two opposite sides a
suitable aerodynamic profile specifically configured for maximizing
efficiency of pressurizing the ambient air during operation. The
metal airfoil is relatively thin at the individual cells 34b for
minimizing airfoil weight while maintaining a continuous structural
loadpath over the entire airfoil for maintaining structural
integrity thereof.
The filler 38 is introduced into the cells to replace the metal
volume otherwise lost by the introduction of the cells themselves
to return the airfoil to the required aerodynamic profile including
the filler 38 in the first side 16. In this way, the airfoil first
side 16 is defined in part by the border 16a directly exposed to
the ambient air, and defined in remaining part by the exposed outer
surface of the filler 38. The hidden portion of the airfoil first
side below the filler 38 defines the several cells 34b and ribs 36
interposed therebetween.
FIG. 3 illustrates in more particularity an exemplary one of the
submerged ribs 36 and the overlying filler 38 exposed to the
ambient air. As indicated above, the filler 38 may be any suitable
material preferably elastomeric for accommodating elastic strain
during operation as the metal airfoil is loaded during operation.
The elastomeric filler 38, such as polyurethane, is preferably
bonded to a primer 40 which first coats or covers the pocket
including its cells 34b and ribs 36. A suitable primer is TyPly BN,
available from the Lord Corporation, Erie, Pa.
As shown in FIG. 4, the filler 38 is preferably flush or
coextensive with the airfoil border 16a, and defines therewith a
continuous aerodynamic surface exposed to the air which is
channeled thereover. The filler 38 thusly adjoins the metal border
16a around the full perimeter 34a of the pocket which directly
exposes to the ambient air the edge of the underlying primer.
A particular advantage of the present invention is that the several
ribs 36 illustrated in FIGS. 1-3 are submerged in the filler 38,
and thusly do not create additional sites where the primer is
exposed to the airfoil surface. Surface exposure of the primer is
thus limited to the perimeter 34a of the pocket illustrated in FIG.
1, with the several ribs 36 being submerged within the filler. In
this way, the perimeter edges of the filler itself are limited in
extent, which correspondingly limits the available filler sites
subject to degradation over life of the blade.
However, submerging the ribs 36 below the filler, and below the
aerodynamic profile defined thereby, correspondingly reduces the
bending moment of inertia of the metal airfoil and its
corresponding strength.
In the preferred embodiment, the ribs 36 are submerged in the
filler to a limited extent in the preferred range of about 0.5-2.5
mm for retaining a relatively thin web or ligament of the filler 38
directly thereatop as illustrated in FIG. 3. In this way, a
continuous surface of the filler 38 is exposed to the ambient air
and defines a major portion of the exposed airfoil first side which
is coextensive with the border 16a as shown in FIG. 1.
However, since the ribs 36 themselves are integral portions of the
metal airfoil, they provide structural integrity of the airfoil
itself and carry substantial loads during operation. Ribs used in
earlier developments of the hybrid blade were exposed at the
airfoil surface for maintaining strength, and would thusly expose
additional primer to the environment. Those early ribs typically
have parallel sides and corresponding sharp corners which effect
considerable stress concentrations and locally increase stress
during operation.
In order to reduce stress concentration, the several ribs 36 each
have an arcuate lateral section or profile as illustrated in detail
in FIG. 3. The rib 36 is generally convex or rounded outwardly
without sharp corners.
Each rib 36 is generally symmetrical in transverse or lateral
section and includes opposite sides which are tapered or sloped
with corresponding side taper angles A measured relative to the
horizontal or generally flat surface of the filler 38. The fib
sides taper smoothly from the rounded apex of the rib to the
relatively flat bottoms of the adjoining cells 34b in a smooth
transition.
The profile of each rib 36 is tapered and blended for several
purposes. Fundamentally, the ribs are provided to separate the
individual cells 34b while maintaining structural integrity of the
metal airfoil. If the taper angle A of the rib sidewalls is too
shallow or small, the volume of the adjoining pockets will be
correspondingly small and weight reduction will be limited. If the
taper angle A is too sharp or large, corresponding interface
stresses between the ribs and filler will increase. And, the side
taper angles may be equal or unequal as desired for minimizing
interface stress and airfoil weight.
Furthermore, the ribs 36 are submerged below the exposed surface of
the filler 38 for maintaining the continuity of the filler as an
aerodynamic surface, yet submergence of the rib correspondingly
reduces the bending moment of inertia of the airfoil section and
can increase stress therein.
Accordingly, the rib apexes are subject to high stress during
operation which is reduced in accordance with one feature of the
present invention by rounding the apexes with corresponding fillets
or radii for eliminating sharp corners.
And, as indicated above, the ribs 36 are submerged below the
exposed surface of the filler in the relatively small range of
about 0.5-2.5 mm to maximize the strength of the airfoil, while
maintaining suitable strength and continuity of the filler ligament
bonded atop the ribs.
Since the several ribs 36 illustrated in FIG. 1 are submerged in
the filler 38, a single pocket 34 is exposed at the airfoil surface
and has the continuous surrounding perimeter 34a. The individual
pocket cells 34b are submerged and hidden from view when filled
with the filler material.
As indicated above, FIGS. 1 and 2 illustrate a typical fan blade
airfoil profile which is relatively thin from leading to trailing
edges. The leading and trailing edges 24, 26 themselves are thin
and sharp and are formed only of the parent metal material for
maintaining strength thereof. The metal airfoil border 16a extends
inwardly from the leading and trailing edges for maintaining
strength of the airfoil edges prior to transitioning into the
adjoining pocket cells 34b.
As shown in FIG. 1, the several ribs 36 are oriented as desired for
providing structural integrity of the airfoil for withstanding the
typical loads experienced during operation which are carried
radially, axially, and torsionally. The loads experienced by the
fan blade during operation may also be caused by foreign object
damage (FOD), such as due to a bird strike typically at the airfoil
leading edge 24.
In order to further increase the structural integrity of the
airfoil having the weight reducing pocket therein, the pocket 34,
as initially illustrated in FIG. 1, preferably includes a submerged
shelf 34c which extends continuously around the pocket perimeter
34a for blending the pocket with the metal border 16a.
A sectional view of the shelf 34c in a preferred embodiment is
illustrated in more detail in FIG. 4. The shelf 34c is tapered at a
taper angle B from the surface of the airfoil border 16a inwardly
into the pockets. In this way, the shelf defines a pronounced slope
or ramp from the pocket edge defining the perimeter 34a and
provides a smooth transition between the airfoil border 16a into
the corresponding pocket cells 34b in which the metal airfoil
decreases in thickness.
In this way, relatively sharp corners or abrupt changes in metal
continuity are reduced or eliminated for correspondingly reducing
stress concentration at the juncture of the filler and the metal
border 16a. The various loads generated during operation of the fan
blade, including bird strike loads, are thusly more efficiently
carried through the metal airfoil between the leading and trailing
edges and from root to tip without pronounced stress concentrations
either around the perimeter of the pocket, or around the perimeters
of the cells 34b thereof or along the individual submerged ribs
36.
As shown in FIG. 1, the shelf 34c is tapered inwardly from the
perimeter 34a of the pocket along the several pocket cells 34b as
well as along the submerged ribs 36 intersecting the pocket
perimeter.
In this way, a distinct shelf 34c is provided continuously around
the pocket perimeter 34a and the metal border 16a for providing a
smooth transition from the metal border into the corresponding
pockets and ribs.
As illustrated in FIG. 4, the shelf 34c has a taper angle B which
is preferably different than the taper angle C of the adjoining
pocket cells 34b at the intersection therewith. The shelf's taper B
is preferably less than the cell taper C thereat to provide a
distinct, generally flat shelf around the full perimeter of the
pocket and adjoining metal border.
The distinct shelf thusly ensures shallow blending of the cells and
ribs at the metal border to reduce stress concentration. And, the
distinct shelf is readily defined in computer controlled machines
for accurate manufacturing thereof.
As shown in FIGS. 3 and 4, the rib taper angle A is also preferably
different than the shelf taper angle B, with the rib taper being
preferably greater than the shelf taper. The rib and shelf tapers
provide different functions, and are correspondingly different in
value. A shallow shelf taper B is preferred to improve the
structural integrity of the metal airfoil and continuity of the
structural loadpaths between the leading and trailing edges, root,
and tip of the airfoil. A larger rib taper is preferred for
maximizing the volume of the adjoining pocket cells 34b for
reducing blade weight, yet without creating unacceptably large
stress concentrations at the ribs themselves.
As shown in FIG. 1, all of the several ribs 36 are preferably
substantially equally submerged in the filler 38 to provide
similarly thick filler ligaments over the ribs as illustrated in
FIG. 3. The submerged ribs blend with the metal border 16a at the
pocket shelf 34c as shown in FIG. 4.
The shelf taper angle B is preferably shallow and less than or
equal to about 20 degrees, and is preferably about 15 degrees for
example. The cell taper angle C at the pocket shelf is slightly
larger than the shelf taper angle B by about 2 to 7 degrees in the
preferred embodiment.
Correspondingly, the rib taper angle A illustrated in FIG. 3 is
preferably less than or equal to about 60 degrees, and is about 20
degrees in the preferred embodiment.
The submerged and tapered ribs provide substantial improvement in
structural integrity of the hybrid fan blade disclosed above
permitting significant weight reduction while maintaining airfoil
strength. Stress concentrations at the ribs are substantially
reduced due to the arcuate profiles thereof, and the tapered
interface between the pocket and the adjoining metal border
therearound further reduces stress concentrations and enhances
structural integrity of the airfoil. The filler bonded into the
multi-cell pocket has a continuous surface exposed to the ambient
air that defines a major portion of the airfoil first side, and
which is coextensive and flush with the surrounding metal border
16a that defines the remaining portion of the aerodynamic surface.
Exposed primer under the filler is limited solely to the pocket
perimeter 34a and substantially reduces sites at which the edges of
the filler may be damaged.
While there have been described herein what are considered to be
preferred and exemplary embodiments of the present invention, other
modifications of the invention shall be apparent to those skilled
in the art from the teachings herein, and it is, therefore, desired
to be secured in the appended claims all such modifications as fall
within the true spirit and scope of the invention.
* * * * *